Low Carb High Fat Diets and the Thyroid

Last year we ran a series on “Zero-Carb Dangers,” which are health problems that can appear if carb intake – or carb+protein intake, since protein can to some degree make up for a deficit of glucose – are too low. Anthony Colpo has recently argued that hypothyroidism should be added to the list of potential zero-carb dangers; and that low-carb high-fat diets in general might create a risk of hypothyroidism. Similar arguments have been made by Matt Stone and others. Our resident thyroid expert, Mario Renato Iwakura, decided to look more deeply into the matter. What does the literature say? Here’s Mario.

There have been anedoctal reports on low carb forums about people becoming hypothyroid after following a low carb, high fat diet. Anthony Colpo recently wrote a blog post about carbohydrate, fat and protein intake and their effects on thyroid hormone levels, concluding that a high fat or high protein diet is detrimental and that a high carbohydrate diet is good for the thyroid [1].

What I will try do demonstrate here is that the sole conclusion we can draw from the literature, including the studies cited by Anthony and others, is that a high polyunsaturated fat (PUFA) diet is detrimental to thyroid health. There is no evidence that a diet, such as the Perfect Health Diet, that is high in saturated and monounsaturated fat, low in PUFA, and provides sufficient, moderate levels of protein and carbohydrate, has any detrimental effect on the thyroid. On the contrary, I believe that such a diet is optimal for thyroid health.

What Has Been Tested: High PUFA Diets

Colpo’s post is extensive and covered most, but not all, relevant studies published to date about the subject. Many of those studies have problems like short duration or calorie restriction. But in almost all, with the exception of one study by Jeff Volek and collaborators [2], the fat used in the high fat diet was predominantly polyunsaturated fat from vegetable oils. An example is the Vermont long term study [3]:

“The long-term study of fat overfeeding included four subjects studied before and after overeating fat for 3 mo. The excess fat in these diets averaged 895 kcal/d consisting of margarine, corn oil, a corn oil colloidal suspension, and fat enriched soups and cookies. The ratio of saturated to unsaturated fatty acids in these diets was ~1:2.5.”

This ratio is precisely that found in corn oil. So, this diet’s fat was probably 13.5% saturated, 29% monounsaturated, and 57.5% polyunsatured.

Or in Ullrich et al 1985 [4]:

“One diet was high in polyunsaturated fat (HF), with 10%, 55%, and 35% of total calories derived from protein, fat, and carbohydrate, respectively.”

Polyunsaturated Fat and the Thyroid.

Let’s look at the literature, starting with two studies not cited by Anthony.

In 1995, Vasquez et al tested four very low calorie diets, with variable amounts of carbs, fats and protein, in 48 obese women for 28 days [5]. All diets were in liquid form, and fat was predominantly PUFA. The composition of the four diets was:

50P/10C

50P/76C

70P/10C

70P/86C

Energy (kcal)

590

590

615

615

Protein (% cal)

35.5

33.7

45.8

43.0

Fat (% cal)

57.8

15.1

48.1

4.1

Carb (% cal)

6.7

51.2

6.1

52.9

T3 Day 0

2.0

2.2

1.6

1.8

T3 Day 28

1.1

1.7

1.0

1.4

Variation

-45%

-23%

-37%

-22%

T3 thyroid hormone levels decreased on all of these severely calorie restricted diets. However, when PUFA was high (50P/10C and 70P/10C) the decrease in T3 was much larger than when PUFA was low (50P/76C and 70P/86C).

In a 1992 paper, Vasquez et al compared two very low calorie diets (600kcal/day), one ketogenic and the other nonketogenic [6]. The fat sources were soybean oil and refined and stabilized vegetable oils.

Ketogenic

Nonketogenic

Protein

35%

34%

Fat

58%

15%

Carbs

9%

51%

T3 Day 0

1.4

1.5

T3 Day 28

0.8

1.3

Variation

-43%

-13%

The various studies cited by Colpo also show decreases in T3 levels in diets high in PUFA. In Ullrich et al 1985 [4], a study of healthy young adults, although TSH, T4, and rT3 did not change significantly, T3 levels on a high polyunsaturated diet decreased more than on a high protein diet:

In the Vermont study [3], where the low carb diet was high in PUFA fat, that was the case too:

“During maintenance eating, levels of T3 (triiodothyronine) were higher on the high-carb diet. When subjects on the low-carb diet began eating the higher-carb mixed weight gain diet, their T3 levels rose. T3 levels among those who went from the high-carb maintenance diet to the mixed diet remained unchanged. In contrast to T3, serum concentrations of T4 were unchanged by overeating or changes in dietary composition.” [1]

Low-PUFA High-Fat Diets and the Thyroid: Lack of Direct Evidence

Unfortunately we don’t have human studies comparing diets high in saturated fat and polyunsaturated fat and their effect on thyroid hormones synthesis. Neither do we have studies showing what happen to T3 levels after a high saturated/monosaturated fat diet is eaten. We will have to rely on indirect evidence.

Indirect Evidence: Calories Required to Maintain Weight.

There is a connection between thyroid activity and obesity. Reduced thyroid activity reduces energy expenditure (“calories out”) and promotes weight gain; normal thyroid function tends to promote normal weight. So we can use the vast number of obesity studies as indirect evidence for the effects of different types of diet on the thyroid.

Anthony emphasized this relationship in his post, noting findings of the Vermont study on overfeeding:

“Again, that both groups gained weight should come as no surprise. However, the group overfed the mixed diet required more calories (2,625 kcal/m2 per day) to maintain their new heavier weights than did the group overfed fat (1,840 kcal/m2 per day). Baseline differences in metabolism between the two groups were ruled out, as there was no difference in total calories required to maintain initial lean weights.”

So the high-PUFA diet promoted weight gain: it caused excess weight to be retained at a lower calorie intake. This is consistent with reduced thyroid activity.

Is this effect due to a high-fat diet generally, or to high-PUFA diets only? Some insight into this question may be found in a blog post by Stephan Guyenet [7]. Rats fed isocaloric diets in which the fat source was varied among three groups – a beef tallow group (primarily saturated fat, 3% PUFA), an olive oil group (primarily unsaturated, 10-15% PUFA), and a safflower oil group (78% PUFA) – had highly variable weight gains. The olive oil group gained 7.5% more weight than the beef tallow group, and the safflower oil group 12.3% more weight. This is exactly the same pattern found in the Vermont overfeeding study in man: reduced energy expenditure as the consumption of PUFA increases.

Since 1945, it has been known that men fed a high carbohydrate and then a high saturated fat diet needed about the same amount of calories to mantain their weight in cold temperature [18]. Here is the data, expressed in terms of the percentage of baseline calorie intake that the men had to eat to maintain their weight:

The high-fat diet consisted largely of butter and cream; the high-carbohydrate diet of extra sugar. When eating the butter and cream, subjects had to eat more calories to maintain weight than when eating the sugary diet – 202% of baseline calorie intake vs 191%. Every subject had to increase calories when eating high-fat. This suggests higher thyroid hormone levels on the high-saturated fat diet than on a high-carb diet.

The Volek Study

Anthony cited a study by Jeff Volek and others [2] on body composition and hormonal responses to a carbohydrate-restricted diet and said that:

Upon commencement of the low-carbohydrate diet a small calorie deficit and a significant increase in protein intake occurred, resulting in a mean 3.3 kilogram fat loss and a 1.1 kilogram lean mass gain. There was a significant increase in total T4 (+10.8%), but for some reason the researchers did not directly measure T3 nor rT3. They instead tested T3 uptake, an indirect measure of thyroxine binding globulin (TBG) in the blood, which tells us little of any real value about changes in actual thyroid hormone levels. The researchers also measured IGF-1, glucagon, total and free testosterone, sex hormone-binding globulin (SHBG), insulin-like growth factor-I (IGF-I), and cortisol. The only significant change noted was a reduction in insulin following the low-carbohydrate diet.

The Volek study is very interesting because it was not calorie restricted (only carbohydrate was restricted) and was done in normal-weight man. The amount of polyunsaturated fat increased a little (from 6 to 11% of calories), but was still low; saturated and monosaturated fats were the main fats of the low carb-high fat diet. Although he did not directly measured T3 nor rT3 we have indirect evidence that they were not impaired.

One very well known fact is that hypothyroid patients, even when taking T4 hormones, usually struggle to lose fat. This occurs because, when thyroid hormones are low, especially when T3 (triidothyronine) is low [8], the basal metabolism is decreased. If the LCHF diet was impairing the thyroid these healthy normal weight men, who had been advised to eat enough calories to maintain their weight during the intervention, should have struggled to lose fat mass. In fact they lost 3.3 kg (7.3 pounds) in 6 weeks on an 8% reduction in calorie intake. The control group did not lose any weight despite an 11% reduction in calorie intake.

More, testosterone levels usually decrease when thyroid hormones are low [9][10]. IGF-1 levels are also decreased in hypothyroidism [11][12]. Glucagon levels are higher in hypothyroid patients [13]. Sex hormone-binding globulin (SHBG) is low in hypothyroidism [14][15][16]. But none of these parameters changed during the LCHF diet.

So this diet which was low in carb (8% of calories) and moderately high in protein (30%) and PUFA (11%) does not seems to affect the thyroid if saturated and monosaturated fat (50% of calories) are the main fat of the diet. Let’s compare the fatty acid profile of the Volek diet with that of human milk:

Saturated

Monounsaturated

Polyunsaturated

Volek diet

41%

41%

18%

Human milk

47.5%

40.5%

12%

Not too much difference. Perhaps PUFA intake needs to be higher than 11% of calories or 18% of fat to impact the thyroid.

Effects of high fat and thyroid responses to cold.

In 1945, Mitchell et al published two articles comparing the effects of proteins versus carbohydrates and fat versus carbohydrate on man’s tolerance to cold exposure [18][19]. Carbohydrate does better than protein, but worse than fat, at maintaining internal temperature as measured by rectal temperature.

On the first experiment, five men consumed a high protein diet (41% P, 40% F, 19% C) and five a high carbohydrate diet (11% P, 41% F, 48% C) for 5.5 months. Food intake was adjusted to mantain a constant body weight.

The effect of decrement in rectal and mean skin temperature during eight hour exposure to cold with light clothing:

Rectal Temp

Skin Temp

High Protein

1.63

5.21

High Carb

1.05

3.65

Significance

P=0.017

P=0.0096

On the second experiment, five men consumed a high fat diet (10% P, 73% F, 17% C) and five a high carbohydrate diet (10% P, 23% F, 67% C) for 56 days. Food intake was adjusted to maintain a constant body weight. The excess fat of the high fat group was provided by butter and cream.

Decrement in rectal temperature from the first two hour to the last two hours of 6 hours exposures to -20º F (-29º C), with variable number of intervening meals:

Number of intervening meals

Difference

0 and 1 meal

Difference

0 and 2 meals

None

One

Two

High Carb

0.71

0.72

0.68

-0.01

0.02

High Fat

0.60

0.36

0.33

0.24

0.27

Significance

None

P=0.034

P=0.018

P=0.083

P=0.051*

P=0.11

P=0.009*

* These probabilities pertain only to the high fat diet

What is clear here, is that 6 hours exposures to -20º F decreased rectal temperature equally in both groups if no meal was ingested. Eating a high carb meal between the intervention did not produced any alteration. But, eating a high fat meal cut the decrement in rectal temperature in half.

So, if a high saturated fat diet maintains body temperature better than a high carbohydrate diet when the body is subjected to cold, it would seem fair to assume that the thyroid functions better on this high saturated fat diet.

Conclusion

A diet with sufficient but not excess protein, moderate carbohydrate comprising a minority of calories, and high intake of saturated and monounsaturated fat but low intake of polyunsaturated fat would seem to be optimal for thyroid function. But this is the Perfect Health Diet!

This is a late reply on this post, but I came across it in trying to understand my unexpected diagnosis of hypothyroidism. I have always been healthy and fit, maintining a lean body mass of 102 lbs on a 5’4″ and about 17% body fat. However, earlier this year, I (1) had my wisdom teeth removed and (2) broke my foot around the same time, so in an attempt to compensate for my temporary downshift in exercising, I went low carb, even going into ketosis for 6 weeks (with 1 day/week of cheat days). Not too long after, I started to inexplicably gain weight, despite a return to training and clean eating with carbs. 6 months later, I’ve been diagnosed with hypothyroidism. Are these events mutually exclusive of each other? I’ll never truly know.

However, I am wondering if I could be provided on insight as to whether or not this is now a permanent condition I will have, or if this is something I can correct in time?

Doctors have been of little help. Because I am not obese, they have little interest in helping me to return to my former lean physique. All they’ve done is prescribe me synthetic thyroid hormones, which actually took a 3rd opinion to finally get a doctor willing to test my hormone levels because I’m still relatively thin compared to most Americans. Hopefully someone here can help?

I don’t believe it’s permanent. Nearly everything will heal. Thyroid issues do take a while usually – months at least. I would just eat and live well and I would expect it to gradually improve. But do eat some carbs.

Some people with early stage hypothyroidism have been able to completely reverse the condition with iodine supplementation. Not the RDA dose (or even the doses Paul recommends here), but higher ones in accordance with Dr. Guy Abraham’s iodine protocol.

Numerous doctors, including David Brownstein and Jorge Flechas, have reported resolution of hypothyroidism (and quite a few other conditions) with the iodine protocol. There is good reason to believe that the modern epidemic of hypothyroidism may be in large part a result of iodine deficiency, and toxicity with the other halides that compete with it, particularly bromine.

The only other interventions I’m aware of that have a track record against hypothyroidism are gluten elimination and LDN therapy.

Personally I doubt carbohydrate per se has much to do with it at a practical level, at least in general, but that’s obviously a matter of debate. Low carb diets do lower free T3 levels, but that appears to be an appropriate and probably healthy physiological adaptation. No one knows what your T3 level should be anyway (some docs think they do). The doctors who have decades of experience with properly formulated low carb and ketogenic VLC diets in thousands of patients have not observed an epidemic of thyroid damage, though perhaps for some people there could be a connection.

Hi Bill,
do you know if any of the doctors you mention have any opinions/recommendations with regards to supplementing with any of the various thyroid drugs or supplements (natural, synthetic, t3, t4, t3&t4…)?

i have been supplementing with iodine, selenium & salt, & now take around 25 mg iodine (4 drops 5% lugol) every other day. along with eating carbs ala PHD.

my morning body temps have slowly climbed, but have now been stalled at around 97.5F for quite a few months now.

so i have been wondering about taking some form of thyroid hormone to get things moving again, i would like to get warmer.
but it seems like there a quite a few different thyroid drug options. & i don’t want to take anything that will impact my current thyroid function ie. affect my own thyroid production (down regulate?).

Darrin, as you probably know this is a highly controversial topic. Conventional docs believe, with incredible assurance, that T4-only therapy is optimal for hypothyroidism. Holistic docs often believe, just as confidently, in giving only pig thyroid extract (e.g., Armour). Some give pure T3.

The best advice by far that I’m aware of comes from my own endocrinologist. (I’m lucky that the best person in the world I could find is in my area.) His approach is highly unconventional and rejects both the T4-only and thyroid extract-only approaches. He has found people on both therapies are often quite miserable in the long run. He finds that the great majority do best on a combination of T4 and low-dose thyroid extract (or T3).

It’s a long story, with much, much more. He has a new book coming out that explains his methods and findings comprehensively:

I’m not convinced body temperature is a great way to assess thyroid function. It’s affected by many things. Low carb diets, for example, lower basal body temp, and that may be extremely healthy in fact. My doc goes by simple labs (TSH and free T4) and much more importantly how the patient feels.

Thank you so much for your replies and feedbacks. It’s been so difficult to get straightforward and objective answers that are free of biases. I have found a new doctor that I am a lot more comfortable with, but she is still anti-T3 medication and seems intent on limiting me to T4 (she feels it’s more stable and wants to encourage the body to convert to T3 on its own); however, we ARE still in the very early stages of the diagnoses and she could change her mind down the line as we see how my body adjusts to the medications. I’ve been started on 50mcgs and told to NOT take iodine supplements, because I live near the coast and the chances of too much iodine are more likely to be had than the chances of not getting enough of it, so she recommended I cease my supplements (which were sold directly to me by my last doc) as the consequences of OD’ing are far too great to risk.

Also, my first doc didn’t test me for antibodies, which the new doc is, so I will soon find out the underlying cause of my hypothyroid, and from there, there could also be further adjustments made to my medications.

One thing to be aware of is that you can cut your T4 tablets into pieces with a razor blade to allow you to test different doses. You want to find the smallest dose that alleviates symptoms. The doctor’s guess of 50 mcg may not be optimal. As your thyroid health improves, you’ll be able to gradually reduce the dose.

That is a great suggestion and definitely one that I will take after my next appointment, and I see how much my levels have changed with the doctor’s methods. Could I have your further suggestion and input on some questions I have regarding that self testing? (1) If I decide to minimally self-increase my doses by adding on, let’s say, 1/4 of a 50mcg pill, how can I avoud running out of my medication early? (2) What do I do after 6-12 months or more if and when I disagree with my doctor’s prescription and chose to increase my doses to reach my desired improvements, then what do I do at the time of my next blood panel and I am face-to-face with my doc?

Well, hopefully your doctor prescribed too much and you will find that a lower dose is best.

If you use a bit more and run out early, your doctor will presumably renew the prescription and/or increase the prescribed dose. I think the thing to do is tell your doctor you used more because you found that (say) 62 mcg worked better.

Probably, because (a) carbs assist recovery, (b) protein assists recovery and protein is often depleted on ketogenic diets, (c) electrolytes assist recovery and are often lost during low-carb and ketogenic diets.

There are things you can do to implement a ketogenic diet in a way that minimizes these risks: eat starches and adequate protein, make ketones with an excess of MCT oil; eat extra electrolytes.

Hello, I have had a thyroid issue, since very young. Thyroidectomy two years ago. Medical care has been poor.. years on compounded thyroid med that did not work. Now on, Porcine Nature-Throid. Adrenals not functioning, ACTH 8, IGF-1 356. Of course feel awful. Reverse T3 20, thyroid pooling in blood. My age is 67, have been organic gardener, active, until last year.

Will your diet address IGF-1? Have been eating high protein, no sugar, home grown organic veggies. Something needs to shift, or I will not make it. Doctor has no clue about this.

IGF-1 is stimulated by high-protein and high-calorie diets, and our diet generally minimizes IGF-1 levels. However I can’t speak to what will happen to IGF-1 in your case specifically because there are diseases like acromegaly which lead to elevated growth hormone and IGF-1 levels due, eg, to pituitary tumors or liver disease.

I think you should try the diet and lifestyle advice in our book. A balanced, nourishing diet will be much better for you then a lean meat and vegetables diet. Circadian rhythm tactics, discussed in Chapter 42, are important for adrenals.

I do not know what specifically is going on in your case and it seems like your doctors ought to be able to do a better job of diagnosis.

I am a South African by birth, In 2006 I moved to Hong Kong from South Africa. In 2011 I moved to the USA from Hong Kong. Since being in the US find that I am constantly feeling very cold. Does moving from one continent to another impact on our bodies.

I use Synthroid 75mcg that I take at 3am my temperature would be between 35.8 and 46 degrees Celcius. I have breakfast at 7 and at 8 take Pantethine for adrenal support. My temperature often drops by 2 degrees. At 1 I take 1/4 grain of Nature Throid that has 9.5 mcg T4, 2.25 mcg T3. My temperature hardly goes up and often drops even more. I do have a pituatory issue as well. Would my rythm be different and should I take my thyroid meds at different time instead of what I am doing. I eat gluten free, paleo and just introduced carbs 3 days ago. Tried iodine but it seems to affect my hashimoto conditon and my thyroid swells up and hurts so I stopped the iodine. I also found the iodine to tank my adrenals making me feel even colder rather than warmer.

Thanks for all you information.
Went to buy your book today but Barnes and Noble were out of stock but hope to have a copy for me by Tuesday next week.

I have been very faithfully on the LCHF diet for 3 weeks. I am not overweight but looking for increased energy levels and improved fitness and training ability. My thyroid has been removed 5 years ago and I am on eltroxin tablets daily. However, the past 5 days my energy level has dropped substantially, I am tired the whole time and my training is terrible. I do mountain biking and train up to 16 hours a week. Now I cannot keep up with my training partners, where I used to be the strongest. My muscles are tired from the start of the training sessions. Any suggestions?

HiTinus! I was very interested to read your post as I have experienced the exact same thing. Although my thyroid has not been removed it appears to hav shrunk to almost nothing. I see you never got a reply to your post but wondered what happened since then? Did you continue with lchf, was it your thyroid or did you find something else was causing your troubles?

You should not be eating LCHF if you lack a thyroid. Rather you should eat PHD proportions, which minimize stress on the thyroid and adrenals. Lacking a thyroid you do not have the same ability other people have to adapt to extreme diets.

Hello Tinus, did you continue with lchf? I am also thyroidless and been Banting for 8 weeks and have really been struggling with my running, to the point where I’m so slow I’m almost too embarrassed to run with my friends anymore. I only wanted to lose 5 kilos and have lost 2 so far but not sure if this lifestyle is worth feeling so crap when I run. Thanks, kim

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